The present invention relates generally to the field of printing devices. More particularly, the present invention relates to an apparatus and method for laminating a print medium in a printer.
Laser printers, copiers, and other similar printing devices mainly include: a photosensitive drum, a developing roller, and a transfer roller or corona wires. In general, in such printing devices, an image is created on the photosensitive drum and then transferred to a sheet of print medium. As used herein, and in the appended claims, the terms xe2x80x9cprinting devicexe2x80x9d or xe2x80x9cprinterxe2x80x9d will be understood to refer to all such devices that output a hardcopy document based on the transfer of an image to a sheet of print medium.
FIG. 1 demonstrates a typical laser-printing device. In a typical printing device, a charging device or corona wire 112 uniformly applies an electrical charge to the outer peripheral surface of a photosensitive drum 120. A laser-generating unit 114 modulates a laser beam 110 based on data defining the image to be printed. The modulated laser beam 110 is then scanned across the outer peripheral surface of the photosensitive drum 120. As a result, a corresponding electrostatic latent image is formed on the surface of the photosensitive drum 120 in the charge pattern.
A developing roller 116 conveys, on its surface, toner that is electrically charged to the same polarity as that of the charge on the photosensitive drum 120. Consequently, the photosensitive drum 120 repels the toner, except where the latent image has been written into the charges on the photosensitive drum 120. The electrostatic latent image on the photosensitive drum 120 is thus developed into a visible toner image by the toner supplied from the developing roller 116.
The developed visible image is then transferred from the photosensitive drum 120 onto a sheet of paper, or other print medium, passing between the photosensitive drum 120 and a transfer roller 122. The transfer roller 122 or corona wires (not shown) transfer a static charge to each sheet of print medium. This charge, in turn, attracts the toner from the photosensitive drum 120 to the print medium causing the image to be transferred to the print medium under pressure from the transfer roller 122.
Once the visible image is on the print medium, the print medium passes through a designated transport path 124 to a fuser 111. When the print medium reaches the fuser 111, it heats the print medium causing the toner to partially melt and stick to the print medium forming a substantially permanent bond.
A number of common applications also call for a protective sheet to cover the printed medium in order to protect the printed medium as well as strengthen and prolong medium life. Traditionally, lamination has served this purpose. A traditional method for laminating a printed medium calls for the printed medium to be removed from the location of the printer and transported to an external laminating device. Once at the lamination device, a pair of lamination sheet members are placed over the printed medium, top and bottom, and pressed at relatively high temperatures to hermetically seal the printed medium.
While traditional methods of laminating printed medium are effective in protecting the printed medium, a number of disadvantages are inherent in traditional methods. Traditional methods require a separate machine to perform the lamination. The use of an extra machine increases the overall cost of the process as well as consumes valuable space. Moreover, the traditional method of laminating requires the additional steps of transporting the printed medium to the laminating device, placing the medium between the lamination sheet members and placing the medium in the laminating device to receive an application of heat and pressure. These additional steps increase both process time and labor.
Efforts have been made to address the shortcomings of traditional laminating methods as demonstrated by U.S. Pat. No. 5,878,303 issued to Endo and by U.S. Pat. Nos. 5,807,461 and 6,022,429 issued to Hagstrom. These efforts have focused on incorporating the use of conventional lamination sheet members in the printing process. FIG. 2 illustrates the current state of the art. Similar to traditional laser printers, a toner-based image is transferred from a photosensitive drum 220 to a print medium. Once the image is transferred to the print medium by a transfer roller 222, laminate sheet members 234 are used to hermetically seal the print medium. In order to surround the print medium, a laminate sheet transport system 230 is implemented immediately after the transfer roller 222. The laminate sheet transport system 230 is made of a transport web 232 which supplies the lamination sheet members 234 to surround the print medium, introduces the print medium between the lamination sheet members 234, and transports the surrounded print medium to a fuser 211 where the lamination sheet members 234 are sealed to the print medium.
While the above-mentioned solutions do allow both printing and lamination of print medium in a single machine, the process sacrifices space by greatly increasing the overall size of the printing device. Additionally, the process increases the complexity of the printing machines by having to address the regulation of the bias voltage of the transfer roller 222 to prevent residual toner located on the photosensitive drum 220 and the transfer roller 222 from transferring onto and marking the lamination sheet members 234.
In one of many possible embodiments of the present invention, a printing apparatus includes a transfer roller for transferring an image to a print medium, a laminating device for substantially covering the print medium with a laminating powder, and a pressing roller to press the print medium after receipt of the image and the laminating powder in order to substantially affix the image and the laminating powder to the print medium.